This invention generally relates to fluorescent lamps and, more particularly, to a method for effectively contacting manganese-activated zinc silicate phosphor with antimony oxide during the deposition of multiple phosphor layers, and the resulting lamp.
Fluorescent lamps are fabricated to provide various color temperatures of emission which generally correspond to the color temperature of a complete or full radiator maintained at the specified temperature. A warm-white correlated color temperature is specified as being about 3000.degree. K. and a cool-white color temperature is specified as being about 4100.degree. K. For illumination in the home, the public normally seems to prefer the warmer color, possibly due to long-time familiarity with the incandescent lamp which has a warm color.
U.S. Pat. No. 3,858,082, dated Dec. 3, 1974 to Thornton discloses various three-component phosphor blends which can be used in fluorescent lamps in order to provide both good color rendition of illuminated objects and a high light output. One embodiment of the phosphor blend which is disclosed in this patent uses apatite-structured strontium chlorophosphate activated by divalent europium as a blue-emitting phosphor component, manganese-activated zinc silicate phosphor as a green-emitting phosphor component and yttrium oxide activated by trivalent europium as a red-orange emitting phosphor component. The relative proportions of these components can be varied to provide the lamp with the predetermined correlated color temperature which can vary over a wide range, although the most popular color temperature for these lamps is about 3000.degree. K. The overall performance of such lamps is excellent, but on occasion the green-emitting phosphor component displays a relatively rapid depreciation of light output, particularly in the vicinity of the electrode, which causes a color shift to occur. Although this normally does not affect the overall performance of the lamp, it can be considered objectionable from an asthetic standpoint.
U.S. Pat. No. 3,937,998, dated Feb. 10, 1976 to Verstegen et al. discloses a three-component phosphor blend for use in fluorescent lamps, in order to provide both good color rendition of illuminated objects and a high light output. The components comprising this phosphor blend are quite expensive and to decrease the amount of these expensive components needed, there is disclosed in U.S. Pat. No. 4,088,923, dated May 9, 1978 to Manders an underlayer of relatively inexpensive halophosphate phosphor of the same emission color, so that the expensive phosphor blend components are "worked harder" and less material is required. A two-layer phosphor coating is also disclosed in U.S. Pat. No. 3,602,758 dated Aug. 31, 1971 to Thornton et al.
It is well known to add a small amount of antimony oxide to a silicate-type phosphor, in order to improve the performance thereof as disclosed in U.S. Pat. No. 2,607,014, dated Aug. 12, 1952 to Roy et al. In U.S. Pat. No. 3,348,961 dated Oct. 24, 1967 to Ropp et al. is disclosed adding a small predetermined amount of finely-divided antimony oxide to the paint used for coating manganese-activated zinc silicate, in order to improve the performance of the fluorescent lamp which incorporates the zinc silicate phosphor.
The internationally accepted procedure for standardizing and measuring the color rendering properties of light sources is set forth in the publication of The International Commission on Illumination, identified as Publication CIE No. 13(E-1.3.2) 1965. More recently, a color-preference index has been proposed for rating the performance of light sources in accordance with what the normal observer considers to be the preferred coloration for familiar objects. This color preference index (CPI) is summarized in the Journal of the Illuminating Engineering Society, pages 48-52 (October 1974) article entitled "A Validation of the Color-Preference Index" by W. A. Thornton.